Conventionally, a hybrid vehicle or an electric vehicle has a motor for traveling, and traveling is accomplished by driving this motor. A battery is therefore required to supply electrical power to the motor, and a high voltage battery of a few hundred volts is normally used in order to efficiently supply electrical power to a high output motor. On the other hand, various components (accessories) operated by electrical power are mounted in the vehicle, and a 12V battery (low voltage battery) is used as a battery for these accessories. High voltage output of the high voltage battery is then stepped down to 12V using a converter to charge the low voltage battery.
Also, in a high rotational speed region of the motor, a counter electromotive force is large, which means that if the voltage applied to the motor is low, maximum torque for the high rotational speed range will become small.
In Japanese Patent Laid-open No. Hei 10-136570, a converter is arranged between a battery and an inverter and a boosted voltage is supplied to the inverter using the converter. It is therefore possible to apply a high voltage from the inverter to the motor, and it is possible to increase maximum torque in a high rotational speed range of the motor. This publication also proposes using a converter as a rectifier for when charging from the outside.
The above publication therefore shows boosting of a battery voltage using a converter and supply of that boosted voltage to a motor. However, this publication simply discloses boosting a supply to a motor and does not consider control of the operation in boosting by the controller.